A standard stud-welding apparatus such as described in my earlier U.S. Pat. No. 4,969,582 has a housing formed with a main throughgoing passage having a rear end connected to a stud feeder and a front end provided with a stud holder. A lateral branch extending backward at a very sharp acute angle from the main passage accommodates a flexible loading element. A stud is fed into the rear end of the main passage, normally pneumatically, to a location somewhat forward of the lateral branch, and then the loading element is moved forward from the lateral branch into the main passage behind the stud to shove it forward so that it ends up in the holder projecting from the front end of the housing.
Typically the housing is provided with a spring-loaded sleeve that coaxially surrounds the front passage end and that has a front edge that typically projects somewhat forward past the stud in the holder. To set a stud the sleeve is pressed against the stud enough to push it against the force of its spring back into the housing so that the fuse tip of the stud can be brought into direct engagement with the substrate. A large electrical current is made to flow between the substrate and the stud to melt the fuse tip, whereby the spring allows the housing to move forward, flattening the melted tip between the stud and the substrate and thereby welding the stud to the substrate.
The disadvantage of this system is that the relatively large mass of the tool must be moved with the stud when its tip is melted to complete the welding operation. The considerable inertia of these elements therefore means that this movement will be somewhat sluggish. As a result the time that it will take the stud to move against the substrate after its tip is melted can be long enough for the tip to partially harden, making a bad weld.